Implant with patient-specific porous structure

ABSTRACT

A method of manufacturing a joint implant for a joint of a specific patient includes obtaining a three-dimensional image of a bone of the joint of the specific patient from medical imaging scans of the bone of the patient and determining on the three-dimensional image a resection plane for contacting a corresponding planar surface of the joint implant for the specific patient. The method includes determining a three-dimensional image of a porous structure of a bone layer along the resection plane from the medical imaging scans of the patient. The joint implant is manufactured with a layer of a patient-specific porous construct attached to the planar surface of the joint implant. The layer of the patient-specific porous construct substantially replicates the porous structure of the bone layer of the specific patient.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application No.13/756,056 filed on Jan. 31, 2013, which claims benefit of United StatesProvisional Patent Application No. 61/594,100 filed on Feb. 2, 2012. Theentire disclosures of each are incorporated herein by reference.

FIELD

This application is directed to orthopedic implants having apatient-specific porous structure.

INTRODUCTION

The present teachings provide various orthopedic implants for jointarthroplasty, such as knee arthroplasty. The implants are designed andconstructed based on three-dimensional digital images of the patient'sjoint. The digital images of the patient's joint can be reconstructedfrom medical scans, such as MRI, CT or X-ray or other imaging scans ofthe patient using commercially available CAD (Computer Aided Design)and/or other imaging software.

According to the present teachings, the porous structure of the bone ofa joint of a specific patient can be determined from the imaging scansof the patient's joint along preoperatively planned resections or otherimplant engagement surfaces. Custom implants for the patient can bedesigned and manufactured to have a patient-specific porous structurethat matches as a mirror surface the patient's porous structure alongcorresponding surfaces of engagement between the implant and the bone ofthe joint of the patient.

SUMMARY

The present teachings provide a method of manufacturing a joint implantfor a joint of a specific patient includes obtaining a three-dimensionalimage of a bone of the joint of the specific patient from medicalimaging scans of the bone of the patient and determining on thethree-dimensional image a resection plane for contacting a correspondingplanar surface of the joint implant for the specific patient. The methodincludes determining a three-dimensional image of a porous structure ofa bone layer along the resection plane from the medical imaging scans ofthe patient. The joint implant is manufactured with a layer of apatient-specific porous construct attached to the planar surface of thejoint implant. The layer of the patient-specific porous constructsubstantially replicates the porous structure of the bone layer of thespecific patient.

The present teachings also provide an orthopedic implant. The orthopedicimplant can be a femoral knee implant. The femoral knee implant caninclude a femoral knee implant core having an interior multiplanarsurface including a plurality of a planar surfaces configured tocorrespond to a plurality of corresponding resection planes of a distalfemoral bone of the specific patient. The femoral knee implant can alsoinclude a patient-specific porous construct including a plurality oflayers attached to corresponding planar surfaces of the femoral kneeimplant. Each layer is constructed to replicate a three-dimensionalporous structure of a bone layer along a corresponding resection planeof femoral bone. The porous structure of the bone layer is determinedfrom medical imaging scans of the un-resected femoral bone.

The orthopedic implant can be a tibial knee implant having a distalsurface configured to correspond to a resection plane of a tibial boneof the specific patient and including a patient-specific porousconstruct. The patient-specific porous construct includes a layerattached to the distal surface of the tibial knee implant. The layer isconstructed to replicate a three-dimensional porous structure of a bonelayer along the resection plane of tibial bone. The porous structure ofthe bone layer is determined from medical imaging scans of theun-resected tibial bone.

Further areas of applicability of the present teachings will becomeapparent from the description provided hereinafter. It should beunderstood that the description and specific examples are intended forpurposes of illustration only and are not intended to limit the scope ofthe present teachings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described herein are for illustrative purposes only ofselected embodiments and not all possible implementations, and are notintended to limit the scope of the present disclosure.

FIG. 1 is a digital three-dimensional image of a patient's femoral bonereconstructed from image scans of the patient and displayed on anelectronic screen according to the present teachings;

FIG. 2 is a digital three-dimensional image of a patient's tibial bonereconstructed from image scans of the patient and displayed on anelectronic screen according to the present teachings;

FIG. 3 is a sectional view of an exemplary femoral implant having abone-engagement layer or surface with a patient-specific porousstructure designed and constructed to match the porous structure of thefemoral bone of the patient along corresponding surfaces or layersaccording to the present teachings;

FIG. 4 is a back view of the femoral implant of FIG. 3 illustratingdifferent porous structures of the bone engagement surface of thefemoral implant according to the present teachings;

FIG. 5 is a digital three-dimensional image of a patient's femoral boneillustrating planned bone resection surfaces corresponding to the boneengagement surface of FIG. 3 for matching porous structures according tothe present teachings;

FIG. 6 is a three dimensional patient-specific porous construct for thebone engagement surface of FIG. 3 and matching the porous structurealong the corresponding surfaces of the femoral bone according to thepresent teachings;

FIG. 6A is a three-dimensional image reconstructed from micro-CT scannershowing a detail of a porous structure of a bone;

FIG. 7 is a top isometric view of an exemplary tibial tray according tothe present teachings;

FIG. 8 is a bottom isometric view of the tibial tray of FIG. 7; and

FIG. 9 is bottom view of a tibial tray showing representative areas ofdifferent porous structures matching corresponding porous structures ofthe tibial bone of the patient according to the present teachings.

Corresponding reference numerals indicate corresponding parts throughoutthe several views of the drawings.

DESCRIPTION OF VARIOUS EMBODIMENTS

The following description is merely exemplary in nature and is in no wayintended to limit the present teachings, applications, or uses. Forexample, although some of the present teachings are illustrated forimplants for a knee joint, the present teachings can be used forimplants of any other joint of the patient, including hip joint,shoulder joint, ankle joint, etc.

The present teachings provide custom-made implants and associatedmanufacturing methods for a specific-patient. Each custom-made implanthas a bone-engagement surface (or surfaces) with a porous layer orporous construct attached thereon. The porous construct has apatient-specific porous structure, i.e. a porous structure that matchesthe three-dimensional porous structure of the bone of the patient alongcorresponding surface (or surfaces) and through a specified thickness,forming a patient-specific porous layer. The porous structure, as usedherein, includes the size, shape, and distribution of pores and variesdepending on location in the bone. The porous structure of the bone ofthe patient along particular surfaces (and extending through a specifiedthickness as a layer) that will engage the implant can be determined byimaging the bone of the patient using imaging scans, such as CT or MRI.The porous structure can be distinguished from a single porosity valuethat can be an average, mean, median, or volumetric measure, such asratio of a volume of interstices or pores of the bone over a volume ofthe mass of the bone.

The porous structure can be obtained from three-dimensional images ofthe patient's bone reconstructed from MRI or CT scans of the patientusing scanners of adequate or desired resolution depending on the imagedanatomy of the patient. For example, commercially available highresolution CT or MRI scanners can be used (hrCT or hrMRI scanners) oreven micro-CT scanners (μCT scanners) with voxel resolution of the orderof a few microns (μm) including, for example, 20 μm, 40 μm or othersize.

Porous structure determination and three-dimensional reconstruction ofbone images from two-dimensional CT or MRI or μCT image data can beobtained using, for example, commercially available software fromMaterialise USA, Plymouth, Mich., such as the Mimics© Innovation Suiteor other vendors. For example, medical imaging data from CT, or MRI orμCT scanners can be segmented to create accurate, patient-specificthree-dimensional models in “STL” or other similar format files. The STLfile format is native to stereolithography CAD (Computer Aided Design)software and can be used for rapid prototyping and computer-aidedmanufacturing. A related file format is AMF (Additive Manufacturing FileFormat), which can support color and multiple materials. The STL or AMFfiles can be also converted to IGES (Initial Graphics ExchangeSpecification) files or other similar format files that are neutral dataformats and allow this digital exchange of information among differentCAD software systems. For example, these digital files can be used withvarious commercially-available CAD software packages for designingcustom and non-custom implants and/or instruments and for planningsurgical procedures.

More specifically, using the above methods, the implants of the presentteachings can be designed and manufactured to incorporate apatient-specific porous construct that matches identically (as a mirrorimage or negative or inverse layer) the porous structure of the bone atsome or all of the bone layers that contact and engage the implant, suchthat the porous structure of the implant is a seamless continuation ofthe porous structure of the bone along the surfaces of contact betweenthe implant and the bone. The patient-specific porous construct can bemanufactured by additive manufacturing technology using instructionsbased on the medical imaging files either directly on the implant orseparately and subsequently attached to the implant or in one integratedmanufacturing procedure.

Generally, in the preoperative planning stage for arthroplasty, imagingdata of the relevant anatomy of a patient can be obtained at a medicalfacility or doctor's office, using one or more of medical imagingmethods described above. The imaging data can include various medicalscans of a relevant portion of the patient's anatomy, as needed forjoint modeling. For knee joint arthroplasty, images of all the kneejoint and, optionally, images of the femoral head or hip joint and anklejoint for mechanical axis determination can be taken. An initialpreoperative plan can be prepared for the patient in image space and caninclude planning and determination for joint resections for receivingcorresponding implants, custom implant design or non-custom implantselection, sizing and fitting and designing patient-specific alignmentand/or resection guides and other instruments for guiding the jointresections, drilling holes for locating pins or other fasteners and forother guidance during the surgical procedure.

The patient-specific porous structures for the implants of the presentteachings can manufactured by casting, welding, laser cutting, moldingor various stereolithography methods, such as, for example, selectivelaser sintering, fused deposition modeling or other rapid prototypingmethods. In some embodiments, the non-porous core of the implant can bemade of a biocompatible metal or alloy, such as titanium, and thepatient-specific porous construct can include, for example, poroustitanium, such as the Regenerex© porous titanium material available fromBiomet Manufacturing Corp., Warsaw, Ind., USA. Exemplary method forcreating porous metal constructs are described in commonly assignedpatent application “Method and Apparatus for Use of Porous Implants”,Ser. No. 11/294,692, filed Dec. 5, 2005 and currently published as US2006/0241775, the disclosure of which is incorporated herein byreference.

Referring to FIGS. 1 and 2, three-dimensional images of bonesreconstructed from medical scans of a specific patient by the imagingand CAD software discussed above are illustrated generically. The boneimages are shown displayed on an electronic screen 52 of a computer 50,such as, for example a desktop, laptop, smartphone, tablet, terminal orother processor communication with an electronic screen 52. In FIG. 1,the bone image 70 is illustrated as an image of distal femoral bone 70.In FIG. 2, the bone image 90 is illustrated as a proximal tibial bone.

Referring to FIGS. 3-6, the present teachings are illustrated for afemoral knee implant 100. The femoral knee implant 100 includes animplant core 103 and a patient-specific porous construct 101. Theimplant core 103 can be non-porous metal or alloy. The implant core 103has an outer (exterior) articulating surface 102 that faces thepatient's knee joint for articulation with the patient's natural tibiaor a prosthetic tibial component. Opposite to the articulating surface102, the implant 100 has an inner bone engagement surface formed by thepatient-specific porous construct 101. In the exemplary embodiment ofFIG. 2, the implant 100 engages the patient's femoral bone along amulti-planar surface, specifically along a plurality of pre-plannedplanar resection planes, as illustrated in the bone image 70 in FIG. 5,in which the images of five resection planes 74, 76, 78, 80 and 82 areshown. The patient-specific porous construct 101 includes acorresponding multiplanar bone engagement surface, including planarsurfaces 124 (124 a, 124 b in FIG. 6), 126, 128, 130, 132. Thecorresponding opposite surfaces of the patient-specific porous construct101 are attached and coincide to corresponding inner surfaces 104, 106,18, 110 and 112 of the implant core 103. In knee implant terminology,resection plane 74 corresponds to a posterior resection, resection plane76 to a chamfer posterior resection, resection plane 78 to a distalresection, resection plane 80 to a chamfer anterior resection, andresection plane 82 to an anterior resection. The corresponding surfacesof the implant core 103 and the porous construct can be similarlyreferenced as posterior (104, 124), posterior chamfer (106, 126), distal(108, 128), anterior chamfer (110, 130) and anterior (122, 132) flangesor planes. The porous construct 101 matches the porous structure of thebone along corresponding layers of thickness “t” as shown in FIGS. 5 and6.

It will be appreciated that the porous structure of the patient-specificporous construct 101 can vary from flange to flange and within a flange,in addition to varying through the thickness of the flange. For example,in the schematic illustration of FIG. 4, different medial and lateraldistal porous structures 138 a, 138 b (corresponding to flange 128 ofthe patient-specific porous construct 101 shown in FIG. 3), anddifferent medial and lateral chamfer posterior porous structure 136 a,136 b (corresponding to flange 126 of the patient-specific porousconstruct 101 shown in FIG. 3) are indicated schematically. Further, theporous structure can vary within each planar section in apatient-specific manner. For example, the anterior chamfer porousstructure 140 (corresponding to flange 130 of the patient-specificporous construct 101 shown in FIG. 3) can decrease or increase along amedial-lateral direction (arrow A), although it can also varynonlinearly, non-monotonically or otherwise for a specific patient.

In the exemplary embodiments of FIGS. 1-6, the patient-specific porousconstruct 101 for the femoral knee implant 100 replicates point-by-pointthe three-dimensional porous structure of the distal femur of a specificpatient over a layer of thickness t along the planned resection planes74, 76, 78, 80 and 82, as obtained from micro-CT scans of the specificpatient or from other medical imaging scans of sufficiently highresolution (hrCT or hrMRI) to show the porous structure of the bone. Inthis example, the resection planes 74, 76, 78, 80 and 82 may be mostlylocated various grades cancellous bone, although some cortical bone maybe involved in some edge locations. Accordingly, the patient-specificthree-dimensional porous construct 101 replicates as a mirror structureand congruently continues the variable porous structure of a layer ofcancellous (and possibly cortical) bone that is uniquely associated withthe specific patient. A detail of the three-dimensional porous structureof a layer of bone is illustrated in FIG. 6A which shows athree-dimensional image of a bone layer reconstructed from atwo-dimensional CT slices using a commercially available micro-CTscanner, as discussed above. The resolution or voxel size used for theimage of FIG. 6A is about 20 μm.

Referring to FIGS. 7-9, the present teachings are illustrated for atibial implant 200. The tibial implant 200 is, for example, a tibialtray having a proximal surface 202 facing the knee joint of the patientand an opposite distal surface 204 on which a patient-specificthree-dimensional porous construct 220 is attached. The tibial implant200 can include various anchoring members for engaging the patient'stibial bone. In the exemplary embodiment of FIGS. 7 and 8, the anchoringmembers include four peripheral pegs 208 configured to engage firmcancellous bone. The peripheral pegs 208 are made of non-porous metaland include a square body terminating at a pyramidal (pointed) tip forinsertion and anchoring into the cancellous bone. The anchoring memberscan also include a central stem 206. In the embodiment of FIG. 8, thecentral stem 206 is tapered, splined and made of non-porous metal.Accordingly, the patient-specific porous construct 220 does not extendto the areas of the distal surface 204 of the tibial implant thatcorrespond to the footprints of the peripheral pegs 208 and central stem206. The tibial implant 200 can include one or more anterior lockingtabs 205 and/or posterior locking tab 207 for engaging correspondinggrooves of a tibial bearing.

FIG. 9 illustrates diagrammatically regions of different porousstructures corresponding to the patient's proximal tibia along aresection plane for receiving the tibial implant 200. For example, aperipheral annular region 232 replicates the porous structure of thepatient's proximal tibial cortical bone. Additionally, regions ofanterior, posterior and medial and lateral different porous structures226, 228, 224 and 230 replicating corresponding tibial bone porousstructures are illustrated. Further, the porous structure within aregion may not be uniform or homogeneous. For example, a local porousstructure 226 may be surrounded by a region of different porousstructure 224. It should also be noted that the porous structure of theareas of the proximal tibia corresponding to the footprints of theperipheral pegs 206 and the central stem will not be replicated in thepatient-specific porous construct 220.

Example embodiments are provided so that this disclosure is thorough,and fully conveys the scope to those who are skilled in the art.Numerous specific details are set forth such as examples of specificcomponents, devices, and methods, to provide a thorough understanding ofembodiments of the present disclosure.

It will be apparent to those skilled in the art that specific detailsneed not be employed, that example embodiments may be embodied in manydifferent forms and that neither should be construed to limit the scopeof the disclosure. In some example embodiments, well-known processes,well-known device structures, and well-known technologies are notdescribed in detail. Accordingly, individual elements or features of aparticular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same embodiment may also be varied in many ways. Such variations arenot to be regarded as a departure from the disclosure, and all suchmodifications are intended to be included within the scope of thedisclosure.

What is claimed is:
 1. An orthopedic implant manufactured for a specificpatient comprising: a femoral knee implant core having an interiormultiplanar surface including a plurality of planar surfaces configuredto correspond to a plurality of corresponding resection planes of adistal femoral bone of the specific patient; and a patient-specificporous construct including a plurality of layers attached tocorresponding planar surfaces of the femoral knee implant, each layerconstructed to replicate a three-dimensional porous structure of a bonelayer along a corresponding resection plane of femoral bone, the porousstructure determined from medical imaging scans of the un-resectedfemoral bone; wherein the patient-specific porous constructthree-dimensionally varies throughout each layer in a patient-specificmanner according to the three-dimensional porous structure of the bonelayer.
 2. The orthopedic implant of claim 1, wherein the plurality ofplanar surfaces includes five surfaces.
 3. The orthopedic implant ofclaim 1, wherein the plurality of planar surfaces includes posterior,anterior and distal surfaces.
 4. The orthopedic implant of claim 3,wherein the plurality of planar surfaces includes posterior chamfer andanterior chamfer surfaces.
 5. The orthopedic implant of claim 1, whereinthe implant core includes non-porous material.
 6. The orthopedic implantof claim 1, wherein the implant core includes an exterior articulatingsurface.
 7. The orthopedic implant of claim 1, wherein the porousstructure is determined from medical imaging scans with a resolution ofa few microns for voxel size.
 8. The orthopedic implant of claim 1,wherein each layer is constructed to replicate a three-dimensionalporous structure of a bone layer along a corresponding resection planeof femoral bone such that the patient-specific construct mirrors theporous structure of the bone layer along the resection planes.
 9. Theorthopedic implant of claim 1, wherein the patient-specific porousconstruct three-dimensionally varies throughout a thickness of eachlayer to correspond to three-dimensional variability of the porousstructure.
 10. The orthopedic implant of claim 9, wherein thepatient-specific porous construct three-dimensionally varies throughouta planar section of each layer to correspond to three-dimensionalvariability of the porous structure.
 11. An orthopedic implantmanufactured for a specific patient comprising: an implant corecomprising: an outer joint-facing surface; and an inner bone engagementsurface having at least one planar surface constructed to correspond toa corresponding resection plane of a bone of the specific patient; and apatient-specific porous construct including a layer attached to theplanar surface of the orthopedic implant, the patient-specific porousconstruct mirroring a porous structure of a bone layer at the resectionplane such that the layer of the patient-specific porous construct is aninverse of the porous structure of the bone layer of the bone at theresection plane.
 12. The orthopedic implant of claim 11, wherein theporous structure is determined from medical imaging scans with aresolution of a few microns for voxel size.
 13. The orthopedic implantof claim 11, wherein the patient-specific porous construct has athickness and the patient-specific porous construct varies within thethickness.
 14. The orthopedic implant of claim 11, wherein thepatient-specific porous construct comprises porous metal.
 15. Theorthopedic implant of claim 11, wherein the implant core comprises: atibial tray comprising: anchoring members extending from the inner boneengagement surface; and locking tabs disposed in the outer joint-facingsurface.
 16. The orthopedic implant of claim 11, wherein the implantcore comprises: a femoral knee implant comprising: an inner boneengagement surface comprising a plurality of planar surfaces constructedto correspond to corresponding resection planes of the bone of thespecific patient; and an articulating surface defining the outerjoint-facing surface.
 17. The orthopedic implant of claim 16, whereineach of the plurality of planar surfaces has a differentpatient-specific porous construct.
 18. The orthopedic implant of claim11, wherein the patient-specific porous construct three-dimensionallyvaries throughout the layer in a patient-specific manner according to athree-dimensional variability of the porous structure.
 19. Theorthopedic implant of claim 18, wherein the layer is constructed toreplicate point-by-point a three-dimensional porous structure of a bonelayer along the resection plane of bone such that the patient-specificporous construct congruently continues the variability of the porousstructure of the bone layer.
 20. The orthopedic implant of claim 19,wherein the porous structure is determined from medical imaging scans ofthe un-resected bone.